1. Field of the Invention
The present invention relates to a power element protection circuit for preventing breakdown of a power element such as a power MOSFET or power bipolar transistor.
2. Description of the Prior Art
Conventionally, one type of power element protection circuit, which is commonly formed on a semiconductor integrated circuit chip, is a thermal shutdown circuit. A thermal shutdown circuit detects temperature with a temperature sensor incorporated therein, and, when the detected temperature is higher than a set temperature, stops the operation of a power element to protect it from thermal breakdown.
Another type of power element protection circuit, which is less commonly used, detects the current that flows through a power element and controls the power element in such a way that the detected current does not become higher than a set current.
A thermal shutdown circuit as described above can be realized with a simple circuit configuration. However, since a power device and a temperature sensor cannot be formed in the same place, when, in particular, transient heat is produced in the power element, there arises a great difference between the temperature detected by the temperature sensor and the temperature of the power element itself. This may cause the thermal shutdown circuit to fail to stop the operation of the power element in time, resulting in thermal breakdown of the power element.
On the other hand, in a power element protection circuit of the type that limits the current that flows through a power element, as the supply voltage becomes higher and thus the voltage drop across the power element becomes greater, the power dissipation in the power element may become so great as to cause thermal breakdown of the power element. An attempt to avoid this by making the set current smaller in case of a high supply voltage, however, may adversely affect the desired operation.